Rock anchors, also referred to as rock bolts, are widely used for example in mining and tunneling for rock reinforcement purposes, in particular to stabilize the wall of a gallery or tunnel. To this end, boreholes usually between two and twelve meters long are driven into a rock face. Rock bolts of corresponding length are then introduced into the boreholes and, depending on the type of rock bolt, are fastened in the borehole by means of grout, synthetic resin adhesives or mechanically, e.g. by clamping or bracing. Well known types of rock bolts are mechanical anchors, e.g. expansion shell anchors, resin rock bolts and so-called SN anchors. Some anchors, such as the SN anchors, are usually fully grouted, i.e. grouted along their entire length in the borehole. Other anchors are only fastened in an end region of the borehole, e.g. by means of resin adhesives or mechanical fastening. Self-drilling anchors, which do not require a predrilled borehole and which usually employ a hollow steel rod as anchor element, are also known. Sometimes, classifying a rock bolt as belonging to a certain type is impossible, as a large variety of rock bolts is known.
An anchor plate is normally mounted onto the end of the anchor element projecting from the borehole and is clamped by means of an anchor head against the rock face. In this way, loads acting in the region of a wall of a gallery or tunnel may be introduced into deeper rock strata. In other words, by employing rock anchors rock strata more remote from the wall may be used for load transmission in order to minimize the risk of collapse of a gallery, tunnel or other structure.